Method of forming a sheet into an integral tube



Jan. 3, 1961 A. w. BARTOSZAK 2,967,139

uusrmon 0F FORMING A swam 'mro AN INTEGRAL TUBE Filed Oct. 9, 1957 INVENTOR.

A. A/ 84 719524 BY Array/rags United States Patent C) METHOD OF FORMING A SHEET INTO AN INTEGRAL TUBE Anthony W. Bartoszak, New York, N.Y., assignor to The Martin Company, a corporation of Maryland Filed Oct. 9, 1957, Ser. No. 689,182 3 Claims. (Cl. 204-1542) The present invention relates generally to the fabrication of tubular fuel elements for use in nuclear reactors, and more particularly to a technique for forming a sheet of core material into an integral tube.

In the copending application of Samuel Storchheim, entitled Techniques for Fabricating Tubular Fuel Elements, Ser. No. 687,493, filed October 1, 1957, now abandoned, there is disclosed a method by which a sheet of core material containing fissionable material is rolled into a tube having a butt joint extending longitudinally therein. The core tube is thereafter clad with inner and outer metal tubes. The assembled components are interfacially bonded by hot-pressing or hot-drawing.

In the copending application of Tibor F. Nagey, Jack A. Hunter and William A. Maxwell, entitled Transportable Nuclear Reactor Power Plant, Ser. No. 684,501, filed September 17, 1957, now abandoned, there is disclosed a nuclear reactor which is adapted to incorporate the tubular fuel element which is the subject matter of the present invention.

In some instances, tubular elements made in the manner described above fail to satisfy certain critical requirements in reactor specifications. This is caused by improper mating of the edges of the core sheet after rolling, such that the resultant seam is irregular and poorly joined.

Upon metallurgical examination of several specimens it was found that the distribution of fuel lacked uniformity at the junction area and that a deficit existed of both core and cladding at localized areas where the core sheet did not join or butt properly. Eccentricity of the core was observed at the area of joining and the amount of nuclear material in this region was either deficient or excessive.

In view of the foregoing,

it is the principal object of the invention to provide an improved technique for rolling a sheet of core material into an integral tube having a joint which is free of the above-noted defects.

More particularly it is an object of the invention to provide a technique for chamfering the edges of a core sheet to be rolled whereby the resultant joint after heat and pressure are applied has a uniform distribution of fuel and is geometrically acceptable.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description to be read in conjunction with the accompanying drawing, wherein like components in the various views are identified by like reference numerals.

In the drawing:

Fig. 1 is a perspective view of a tubular fuel element.

Fig. 2 is a transverse section taken through a sheet of core material before rolling into tubular form.

Fig. 3 is a transverse section taken in the plane indicated by line 3-3 in Fig. 1.

Fig. 4 is a transverse section taken through a hotpressing die for bonding the tubes.

Referring now to Fig. l, a tubular element in accord- 2,967,139 Patented Jan. 3, 1961 ice ance with the invention comprises a tube 10 of core ma terial'clad by inner and outer tubes 11 and 12. The core 10 may be formed by a rectangular sheet of sintered material constituted by particles of uranium oxide or other nuclear fuel dispersed in a matrix of metal powder such as aluminum or stainless steel. formed of standard tubing, same as the matrix metal.

The longitudinal seam line 10a in Fig. 1 represents the juncture point of the butting edges of the core sheet after it is rolled into tubular shape.

In order to obtain a bonded joint free of imperfections, in accordance with the invention the longitudinal edges 13 and 14 of the core sheet are chamfered by filing or other means. The edges have complementary angles of inclination such that when the sheet is rolled into tubular form over a mandrel, the edges mate perfectly. The juncture line 10a is at an angle displaced from the radial line of the tube. Consequently when radial pressure is applied to the tube in subsequent hot-pressing or drawing, compressive forces are applied to the mating edges to effect a bond therebetween, thereby producing an integral tube.

The filing angle may be adjusted to fit various rolled core diameters and working jigs may be provided to maintain the filing angle constant for a given core diameter.

After the core is rolled and the clad tubes are assembled thereon, the assembly is placed in a split die 15 as shown in Fig. 4. Also included is a central mandrel 16 and a sacrificial tube 17 which surrounds the assembly, the tube serving as an envelope for evacuating the assembly and also as a protective cover during hot-pressing.

A cylindrical cavity is formed in the die parts, the cavity being divided between the die halves. The die parts are internally heated by electrical elements 18 and subjected to pressure. The dimensions of the cavity are somewhat smaller than the assembly. Thus, when pressure is applied, the compressive forces produce metallurgical bonds between the interfacial boundaries of the core tube and the cladding tubes and at the same time the bevelled edges 13 and 14 of the coretube are joined together. This operation is preferably carried out in vacuo. The assembly is then removed from the die, the sacrificial cladding is peeled off, and the mandrel withdrawn.

It is to be understoodthat the use of a core sheet having chamfered edges which are joined together when the sheet is rolled is not limited to subsequent hot-pressing operations. The invention may also be used with hotdrawing or other techniques for effecting interfacial bondthe metal thereof being the ing of the tubular assembly.

While there has been shown what is considered to be a preferred embodiment of the invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims to cover all such changes and modifications as fall within the true scope of the invention.

What is claimed is:

1. The method of fabricating an integral tubular fuel element comprising the steps of assembling a hollow cermet core containing particles of an oxide of a fissionable metal dispersed in a metal matrix with inner and outer cladding tubes, said core being formed of a rectangular sheet having bevelled longitudinal edges with complementary angles of inclination, said sheet being rolled into tubular form with the complementary edges mated, and subjecting said assembly to heat and pressure to cause interfacial bonding.

2. The method of fabricating an integral tubular fuel element comprising the steps of assembling a hollow cermet core containing particles of an oxide of a fission- The cladding tubes are.

3 r able metal dispersed in a metal matrix with inner and outer-cladding tubes, said core beingformed of 2. rectangular sheet having bevelled longitudinal edges with complementary angles of inclination, said sheet being rolled into tubular form with the complementary edges mated and hot-drawing said assembly to cause interfacial' bonding ofthe components', wher.eby said edges are joined along a'uniform line of juncture.

3'. The method of fabricating an integral tubular fuel element comprising the steps of assembling a hollow cermet core containing particles of an oxide of a fissionable metal dispersed in a metal matrix with inner and outer cladding tubes, said core being formed of a rectangular sheet having beVeIledlOngitudinaI edges with complementary angles of inclination, said sheet being rolled into tubular form with the complementary edges filmed, and die-pressing said assembly at an elevated tempeiratu-re to. cause. interfacial bonding of the components,

whereby said edges are joined along a uniform line of juncture.

References Cited in the file of this patent UNITED STATES PATENTS 682,423 Patterson Sept. 10, 1901 2,197,191 Nichols et al. Apr. 16, 1940 2,768,433v CID nn el, Oct 30 1956 2,805,473 Handwerk etv a1 Sept. 10, 1957 FOREIGN PATENTS,

754,559 Great Britain Aug. 8, 195

OTHER REFERENCES I. International'Conf. on Peaceful Uses of Atomic Energy, vol. 3, 1955, p. 216.

II. International Conf. on Peaceful Uses of Atomic Energ vol. 9, 19,55,,pp. 196-202. 

1. THE METHOD OF FABRICATING AN INTEGRAL TUBULAR FUEL ELEMENT COMPRISING THE STEPS OF ASSEMBLING A HOLLOW CERMET CORE CONTAINING PARTICLES OF AN OXIDE OF A FISSIONABLE METAL DISPERSED IN A METAL MATRIX WITH INNER AND OUTER CLADDING TUBES, SAID CORE BEING FORMED OF A RECTANGULAR SHEET HAVING BEVELLED LONGITUDINAL EDGES WITH COMPLEMENTARY ANGLES OF INCLINATION, SAID SHEET BEING ROLLED INTO TUBULAR FORM WITH THE COMPLEMENTARY EDGES MATED, AND SUBJECTING SAID ASSEMBLY TO HEAT AND PRESSURE TO CAUSE INTERFACIAL BONDING. 